When Is Post Weld Heat Treatment (PWHT) Necessary?

When Is Post Weld Heat Treatment (PWHT) Necessary?

Carrying out a Post Weld Heat Treatment (PWHT) in many cases will keep the material strong while maintaining durability.

 

Post weld heat treatmentExtreme heat caused by welding may reduce the flexibility and durability of materials and post weld heat treatment (PWHT) is a technique of changing properties of metals that removes the stresses by putting the microstructures back to its original state and renders it to be stress-free. The post weld heat treatment (PWHT) is also known as “stress relief” because the method consists of holding a specific temperature long enough to achieve the desired reduction in residual stresses. This process improves the ductility and metallurgical structure of the materials and reduces the risk of brittle fracture, to name some of its benefits. 

This technique is a common practice and requires special attention in temperature selection because an inaccurate temperature can cause major problems, such as the depletion of weld strength. Deciding when to use post-weld heat treatment service depends on the composition of the weld and base materials, end use or service of the product and the prior thermal and mechanical processing of the base metal.

In Australia, each standard chooses a specific thickness for the mandatory use of this method. However, there are specific factors that are likely to contribute to the residual stress of your material and make the need for a PWHT.  For example, if you are welding two different materials together, the structure of one of the original elements can suffer some changes. In this case, a Post Weld Heat Treatment (PWHT) may be necessary. 

As a rule the thicker the weld, the higher the thermal gradient which may contribute to higher residual stress on the primary material making a Post Weld Heat Treatment (PWHT) required. To avoid changes in structure caused by cooling too fast, consider using a PWHT as cooling temperatures can increase rather than reduce the strength of certain steels.

While a PWHT may be necessary in many cases, it’s important to remember that a post weld treatment may also cause irreparable damage if administered inaccurately. It is crucial for the safety of your clients and the reputation of your company that you always make sure that you have the assistance of heat treatment specialists

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